Science Research 2015; 3(6): 300-303

Published online December 25, 2015 (http://www.sciencepublishinggroup.com/j/sr)

doi: 10.11648/j.sr.20150306.16

ISSN: 2329-0935 (Print); ISSN: 2329-0927 (Online)

Film Formation and Characterization of Undoped ZnO on M-plane Sapphire by Mist Chemical Vapour Deposition (Mist-CVD) with Different Carrier Gas Flow Rates

Hla Myo Tun1, Thant Zin Win

2, Kensuke Minami

3, Satomi Teraya

3, Koushi Okita

3,

Yusui Nakamura3, 4

1Department of Electronic Engineering, Mandalay Technological University, Mandalay Region, Republic of the Union of Myanmar 2Department of Electronic Engineering, Yangon Technological University, Yangon, Myanmar 3Graduate School of Science and Technology, Kumamoto University, Kumamoto, Japan 4Kumamoto Institute for Photo-Electro Organics, Kumamoto, Japan

Email address: hmyotun@gmail.com (H. M. Tun)

To cite this article: Hla Myo Tun, Thant Zin Win, Kensuke Minami, Satomi Teraya, Koushi Okita, Yusui Nakamura. Film Formation and Characterization of

Undoped ZnO on M-plane Sapphire by Mist Chemical Vapour Deposition (Mist-CVD) with Different Carrier Gas Flow Rates. Science

Research. Vol. 3, No. 6, 2015, pp. 300-303. doi: 10.11648/j.sr.20150306.16

Abstract: ZnO thin films were deposited on sapphire substrate by mist chemical vapor deposition (mist-CVD) with different

flow rate of carrier gas. This is a simple and low cost method for large-area deposition system. In this experiment, zinc chloride

solution was used as sources, and the crystal growth was achieved at the growth temperature of 600°C and various flow rates of

Nitrogen gas. The X-ray diffraction (XRD) spectrum was performed, and the photoluminescence spectra proved near-band-edge

emission and strong deep-level emissions. In this work, we obtained the optimum condition for crystal growth of ZnO on

m-plane sapphire, where XRD θ-2θ single peak at m-plane ZnO.

Keywords: Film Formation, Characterization, Mist-CVD, ZnO, LED

1. Introduction

In recent times, II-VI semiconductor materials have been of

great interest due to application for luminescence and ultraviolet

(UV) optical devices such as light emitting diodes (LEDs) and

laser diodes (LDs) [1]. Zinc Oxide (ZnO) has fascinated

extensive consideration due to its greater physical properties and

potential technological applications. The wide direct-bandgap of

ZnO is 3.37eV and it has a large exciton binding energy of

60meV, which errands efficient excitonic emission processes at

room temperature and enables devices to purpose at a low

threshold voltage. ZnO (as a group-II oxide) proves enormous

assure for applications in blue/UV light emitters and

photodetectors, over and above transparent electronics, chemical

sensors, spintronics, and varistors. Various techniques, such as

magnetron sputtering, reactive evaporation, pulse laser

deposition (PLD), metaorganic chemical vapor deposition

(MOCVD), molecular bean epitaxy (MBE), spray pyrolysis, and

sol-gel can be useful for ZnO thin films deposition [2].

We have developed a mist-CVD method as a promising

technique that allows superior controllability in film deposition

at low cost with an uncomplicated system and low energy

consumption [3]. In this method, a 60ml of zinc chloride (zinc

compound) solution is ultrasonically atomized to form mist

particles of the solution, and the particles are afterward

transferred by a carrier gas of nitrogen onto the heat sapphire

substrate, forming ZnO film by pyrolysis and chemical

reactions. The fundamental concept may be similar to that of

spray pyrolysis, but the main difference is in particle volume

and the merits of treating mist particles like nitrogen gas.

In this paper, we report that ZnO layers deposited on

m-plane sapphire substrate by mist chemical vapor deposition

(mist-CVD) with different flow rate of carrier gas at

600°Cexperiments. The optical and structural properties of

un-doped ZnO layer are characterized by scanning electron

microscopy (SEM), photoluminescence (PL), film thickness

measurement and X-ray diffraction (XRD). Based on the

results, it is confirmed that ZnO films have single orientation

of crystal.

Science Research 2015; 3(6): 300-303 301

2. Experiment

Fig.1 shows the experimental setup of mist-CVD system for

crystal growth of undoped ZnO films were grown on m-plane

sapphire with different flow rate of carrier gas. Deposition of

ZnO thin films was carried at the substrate temperatures of

600°C with various gas flow rates of 6 L/min, 8 L/min and 10

L/min and 60 mL of zinc chloride solution.

Fig. 1. Experimental Setup.

The photoluminescence spectra were verified by using

He-Cd Laser which has an excitation wavelength of 325nm.

After the thin film was etched by mixed solution of

CH3COOH solution, phosphoric acid and pure water and the

film thickness was measured by KLA-Tencor. The surface of

film morphology was investigated with JEOL JSM7600F

(SEM). The X-ray Diffraction (XRD) scan in the θ/2θ mode

was performed to determine the film orientation perpendicular

to the film surface.

3. Results and Discussions

The deposition condition for experiment is given in Table I.

Table I. Deposition Conditions for Experiment.

Solution Zinc Chloride aqueous solution (0.1 mol/L)

Deposition Temperature 600°C

Flow Rate 6 l/min, 8 l/min and 10 l/min

Substrate m-plane Sapphire

Solution Amount 60ml

Fig.2 shows the photographs of deposited thin films of ZnO

at substrate temperature of 600°C with different flow rates for

6 L/min, 8 L/min and 10 L/min of nitrogen gas. The surface

morphologies were characterized by SEM. In case of sample

grown at 8 L/min and 10 L/min of flow rate, the front side of

the sample has almost no grain boundary.

In order to characterize the optical properties of ZnO films

deposited on m-plane sapphire, the PL measurements were

performed at room temperature and the results are revealed in

Fig.3. A weak near-band-edge (NBE) emission peak was

observed at 3.26eV, while the deep level emission at 2.48eV

which is related to oxygen vacancy [4-10].

In order to characterize the crystallinity of ZnO thin films,

XRD analyses were performed and the results are shown in

Fig.4. From the XRD spectrum for the sample grown with the

flow rate of 6 L/min, c-plane ZnO (002) at 31.7°, r-plane (101),

m-plane (002) at 66.3° and sapphire (100) diffraction peaks

were shown. But the other two samples grown with flow rates

of 8 L/min and 10 L/min possess m-plane (100), m-plane (200)

and sapphire.

(a) (b) (c)

(d) (e) (f)

Carrier Gas Flow Rate

of 6 L/min

Carrier Gas Flow Rate

of 8 L/min

Carrier Gas Flow Rate

of 10 L/min

1µm

2 Inches

Fig. 2. Photograph and SEM Images are Shown in (a)-(c) and (d)-(f), Respectively.

302 Hla Myo Tun et al.: Film Formation and Characterization of Undoped ZnO on M-plane Sapphire by

Mist Chemical Vapor Deposition (Mist-CVD) with Different Carrier Gas Flow Rates

(a) Carrier Gas Flow

Rate of 6 L/min

(a) Carrier Gas Flow

Rate of 8 L/min

(a) Carrier Gas Flow

Rate of 10 L/min

Fig. 3. Photoluminescence Spectra for the Samples Grown with Carrier Gas Flow Rate of (a) 6 L/min, (b) 8 L/min and (c)10 L/min.

The film thickness results are shown in Fig.5. When the

clod mist come into the furnace, then the temperature of the

mist increase with the location on the substrate. So, the

thickness increases with the location because the thermal

reaction is enhanced by the mist temperature. When we

increased the flow rate from 8 L/min to 10 L/min, the

decomposition of the mist is decreased because the

temperature of the mist is not increased at the high flow rate.

According to these responses, the crystal growth condition for

the sample grown with the carrier gas flow rate of 8 L/minis

was found to be optimal. The summary table for experiment is

given in Table II.

(a) Carrier gas Flow

Rate of 6 L/min

m-plane

(100)

c-plane

(002)

r-plane

(101)

r-plane

(102)

a-plane

(110)

m-plane

(200)

Sapphire

m-plane

(100) m-plane

(200) Sapphire

(b) Carrier gas Flow

Rate of 8 L/min

(c) Carrier gas Flow

Rate of 10 L/min Fig. 4. XRD Spectra for the Samples Grown at Various Flow Rates.

Fig. 5. Film Thickness Measurement for 550°C, 600°C and 650°C.

6 L/min

10 L/min

8 L/min

Fig. 6. PL Measurement for Front Side of the Sample on 550°C, 600°C and

650°C.

Science Research 2015; 3(6): 300-303 303

Table II. Summary for Experiment.

Film Thickness PL SEM XRD

6 l/min Large Weak Rough Multi-peak

8 l/min Large Strong Flat Multi-peak

10 l/min Small Weak Flat Only m-plane

4. Conclusion

In this paper, undoped ZnO grown on sapphire by

mist-CVD technique has been characterized. The undoped

ZnO on m-plane sapphire was growth with different flow rate

of carrier gas at 600°C. From the PL measurement, weak

near-band-edge (NBE) emission peak was observed at 3.26eV

while the deep level emissions were very strong. Film

thickness decreased with the flow rate. According to this

experiment, the optimum values for mist CVD techniques of

undoped ZnO with m-plane sapphire are substrate temperature

of 600 °C and the carrier gas flow rate of 8 L/min. In this work,

we found the optimum condition for crystal growth of ZnO on

m-plane sapphire and single orientation of m-plane ZnO was

observed by XRD θ-2θ scanning mode.

Acknowledgements

The authors sincerely acknowledge Dr. Hiroshi Shirakawa

for valuable discussions. This work is supported for EEHE

Project from Japan International Cooperation Agency

(JICA).

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